Removable external filter for servo air actuated valves

ABSTRACT

An example filter assembly prevents particles from entering a control valve and defines an airflow path between an inlet and outlet. An inlet tube extends from an inlet and defines an inlet passage into a filter housing. Openings within the inlet tube open into an interior space of a filter housing. An outer housing defines a cavity within which the filter housing is secured. The filter housing includes an open top portion that engages a cap that covers and seals the outer housing. The cap holds the filter housing to prevent movement of the filter housing.

BACKGROUND

This disclosure generally relates to a filter element for preventingcontaminant intrusion into working parts. More particularly, thisdisclosure relates to a filter element to block particles in acontrolled airflow from reaching an actuator.

Airflow is utilized and controlled for many reasons and by manydifferent methods and actuators. In most applications it is required toprevent particles and other foreign matter from entering the actuator.In many instances the actuator operates a shaft that in turn moves acontrol disc or flap that is positioned within the airflow. Filtersutilized to prevent contaminant intrusion are selected to preventspecific sized particles from entering the critical parts of theactuators. The filter can become clogged quickly if opening sizes areexcessively small and therefore require frequent changes. However, afilter with large openings may not capture sufficient particles toprovide the desired protection of the actuator. Moreover, a cloggedfilter can affect operation of the control valve and restrict airflow.

SUMMARY

A disclosed filter assembly prevents particles from entering a controlvalve and defines an airflow path between an inlet and outlet. Theexample filter assembly includes an inlet tube that extends from aninlet and defines an inlet passage into a filter housing. Openingswithin the inlet tube open into an interior space of the filter housing.An outer housing defines a cavity within which the filter housing issecured. The filter housing includes an open top portion that engages acap that covers and seals the outer housing to hold the filter housingand prevent movement of the filter housing.

The example filter assembly filters particulates from the airflowcommunicated to the control valve and also defines the airflow passagebetween the inlet and the outlet. During filter replacement particulatematter is prevented from falling into the inlet passageway by the inlettube extending from the inlet opening. Accordingly, the filter housingcan be removed and replaced without particles falling into the inlet.

These and other features disclosed herein can be best understood fromthe following specification and drawings, the following of which is abrief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an example pneumatically driven air controlvalve.

FIG. 2 is a perspective view of the example pneumatically driven aircontrol valve.

FIG. 3 is a cross-sectional view of an example external filter mountedwithin an example control passage.

FIG. 4 is an enlarged cross-sectional view of an example capconfiguration of the example external filter.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, a portion of an example pneumatically drivenair control valve is schematically shown at 10 and includes a controlvalve assembly 12 for controlling airflow through a main passage 14. Thecontrol valve assembly 12 includes an actuator 16 that utilizes aportion of air tapped from the main airflow 15 through the main passage14. A control passage 18 directs air to a torque motor 20 to modulate apiston 24 that in turn controls a position of a valve plate 22. Thevalve plate 22 is disposed within the main passage 14 to control themain airflow 15. The example torque motor 20 controls a pressuredifferential across the piston 24 that is mechanically linked to movethe valve plate 22 between an open and closed position that produces adesired airflow through the main passage 14. It should be understood,that although an example control valve configuration is disclosed by wayof example, other valve configurations would also benefit from thisdisclosure.

A filter assembly 26 is disposed within the control passage 18 to blockparticles and other contaminants from reaching the torque motor 20 andpiston 24. As appreciated, particles and other contaminants presentwithin the airflow 15 can build up within the torque motor 20 and hamperdesired operation. Accordingly, the filter assembly 26 blocks suchparticles and contaminants from reaching the torque motor 20.

The example filter assembly 26 is mounted through an external port 25 ofthe control valve assembly 12. The filter assembly 26 can therefore beaccessed and removed periodically for maintenance.

Referring to FIG. 3, the example filter assembly 26 is disposed withinthe control passage 18 and defines an airflow passage between an inlet28 and an outlet 30. The example inlet 28 is disposed about an axis 32and the outlet 30 is transverse to the inlet 28. The inlet 28 and outlet30 open into a chamber 34 that receives the filter assembly 26. Thechamber 34 includes a diameter greater than the inlet 28 into which thefilter assembly 26 is received. As appreciated, although the examplechamber 34 is cylindrical, the chamber 34 could be any shape to receivethe filter assembly 26.

An inlet tube 36 extends from the inlet 28 into the chamber 34 anddefines an inlet passage into a filter housing 38. The inlet tube 36 isdisposed along the axis 32 common to the inlet 28. The inlet tube 36includes an outer diameter 40 that is smaller than the chamber 34 suchthat a space is defined between the inlet tube 36 and the chamber 34.The inlet tube 36 includes openings 42 that open within the filterhousing 38, but not within the chamber 34. Therefore, airflow from theinlet 28 is directed into the filter housing 38 and not into the spacedefined between the inlet tube 36 and the chamber 34.

An outer housing 44 is mounted to the chamber 34 and extends from thechamber 34 to define a cavity within which the filter housing 38 issecured. A seal 45 seals the interface between the outer housing 44 andan inner surface of the chamber 34. The filter housing 38 includes anopen top portion 48 that engages a cap 50 that covers and seals theouter housing 44. The cap 50 includes an internal lip 52 that holds thefilter housing 38 in a desired orientation within the outer housing 44.A first seal 54 is supported on the lip 52 and seals against an innersurface of the filter housing 38. The example internal lip 52 isconcentric about the axis 32 and matches the inner diameter of thefilter housing 38. The example desired orientation of the filter housing38 is spaced apart from an inner surface of the outer housing 44 todefine an annular chamber 70.

A bottom portion 60 of the filter housing 38 includes a recess 58 thatreceives a shoulder 62 of the inlet tube 36. The shoulder 62 includes aseal 46 that seals against an inner surface of the recess 58. Moreover,the shoulder 62 holds the bottom portion 60 of the filter housing 38spaced apart from an inner bottom surface of the outer housing 44. Thespaced apart orientation of the filter housing 38 relative to the outerhousing 44 provides an airflow passage 72 that communicates outgoingairflow from the filter housing 38 to the chamber 34.

The filter housing 38 includes a filter medium 56 through which air fromthe inlet tube 36 flows. The filter medium 56 comprises at least onefilter having a plurality of openings of a desired size and density. Thenumber of openings and density provide a desired porosity to filter, orblock the flow of particles of a set size from flowing through thefilter medium 56. Moreover, the filter medium 56 is selected to balanceany restriction to airflow with the removal of particulate matter fromthat airflow. In other words, the filter medium is selected such thatany restriction to airflow is within desired operating parameters.

The example filter medium 56 comprises a wire mesh fabric that issupported on the filter housing 38. The filter housing 38 supports thewire mesh fabric about the outer circumference. The wire mesh fabricprovides a desired air flow area along with a minimum opening size toblock the flow of particles of a defined size. As appreciated, othermaterials for forming the filter medium 56 are within the contemplationof this disclosure.

Referring to FIG. 4 with continued reference to FIG. 3, the examplefilter medium 56 includes a first filter 64 that has a first porosityand a second filter 66 that has a second porosity different than thefirst porosity. In the disclosed example, the first filter 64 comprisesporosity larger or courser than that of the second filter 66 such thatthe first filter 64 will catch larger particles while the second filter66 will catch smaller particles not blocked by the first filter 64. Thefirst filter 64 is disposed on an inner most radial surface of thefilter housing 38 such that airflow will first flow through the firstfilter 64. The second filter 66 includes smaller openings and thereforewill retain particles much smaller than those initially caught by thefirst filter 64. The second filter is 66 is disposed about the firstfilter 64 and on an outermost surface of the filter medium 56. It shouldbe understood that the filter medium 56 can also include one filter witha single porosity, or several filter layers as desired.

The cap 50 includes the first seal 54 that seals against an innersurface of the filter housing 38 and a second seal 55 that seals the cap50 against an inner surface of the outer housing 44. A securing member68 holds the cap 50 against the top portion of the filter housing 38.Moreover, the cap 50 holds the filter housing 38 against the shoulder 62of the inlet tube 36 (FIG. 3) to prevent movement of the filter housing38 relative to the outer housing 44.

The example filter assembly 26 filters particulates from the airflowcommunicated to the control valve assembly 12. The example filterassembly 26 also defines the airflow passage between the inlet 28 andthe outlet 30. The airflow passage begins with airflow flowing throughthe inlet 28 into the inlet tube 36. Air within the inlet tube 36 exitsthrough openings 42 of the inlet tube 36 into an interior space of thefilter housing 38. Airflow then passes through the first course filter64 and the second finer filter 66 into the chamber 70 disposed about thefilter housing 38. The chamber 70 is annular and concentric about theaxis 32 and the filter housing 38.

Airflow from the chamber 70 flows under the filter housing 38 into thepassage 72 between the bottom portion 60 of the air filter housing 38and the outer housing 44. The space between the filter housing 38 andthe outer housing 44 provides the path for communicating air into thechamber 34 defined about the inlet tube 36. The chamber 34 is annularand concentric about the inlet tube 36 and communicates airflow with theoutlet 30. Air through the outlet 30 is then flowed to the torque motor20 (Best shown in FIGS. 1 and 2). Accordingly, not only does the examplefilter assembly 26 block particulate flow, but it also defines the flowpassage between the inlet 28 and the outlet 30.

The inlet tube 36 includes a bottom shoulder 76 that fits over theopening to the inlet 28. The shoulder 76 includes a seal 78 thatseparates incoming airflow from outgoing airflow. During filterreplacement, particulate matter that may fall from the filter housing 38toward the inlet 28. None of these particles can fall into the inlet 28because the inlet tube 36 includes no openings near the inlet 28.Accordingly, the filter housing 38 can be removed and replaced withoutparticles falling into the inlet 28.

The disclosed example filter assembly 26 provides a removable air filterto block particles from entering the control valve assembly 12, whilealso protecting against contaminant intrusion into the control passage18 during replacement of the filter medium. The example filter assembly26 also defines the passage between the inlet 28 and outlet 30.Moreover, the example filter housing 38 is positively held in place suchthat a build up of particle matter does not create airflow leaks aroundthe filter medium 56.

Although an example embodiment has been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of this disclosure. For that reason, the followingclaims should be studied to determine the scope and content of thisinvention.

1. A filter assembly comprising: a filter housing defining an innercavity and an inlet; a filter medium defining an outer periphery of thefilter housing; an air inlet tube extending through the inlet into theinner cavity; and an outer chamber defined about the outer periphery ofthe filter housing receiving airflow through the filter medium.
 2. Thefilter assembly as recited in claim 1, including an outer housingdisposed about the filter housing defining an outer wall of the outerchamber, wherein the outer chamber is defined between the outerperiphery of the filter housing and the outer housing.
 3. The filterassembly as recited in claim 2, wherein the filter housing includes abottom surface spaced apart from the outer housing that defines anairflow passage to the air inlet tube.
 4. The filter assembly as recitedin claim 3, wherein the air inlet tube includes a shoulder for holdingthe outer housing spaced apart from the bottom surface of the outerhousing.
 5. The filter assembly as recited in claim 1, wherein the airinlet tube includes openings for communicating air to the inner cavityof the filter housing.
 6. The filter assembly as recited in claim 1,including a cap secured to one open end of the outer housing, the capengaged to hold the filter housing in a desired position relative to theouter housing.
 7. The filter assembly as recited in claim 1, includingan inlet seal disposed between the air inlet tube and an inlet bore. 8.The filter assembly as recited in claim 1, wherein the air inlet tube isdisposed along an axis, the filter housing is concentric about the axis,and the outer chamber is an annular cavity defined about the axisbetween the filter housing and the outer housing.
 9. The filter assemblyas recited in claim 1, wherein the filter medium comprises a firstfilter having a first porosity, and second filter including a secondporosity different than the first porosity.
 10. The filter assembly asrecited in claim 9, wherein the first filter defines an inner mostsurface of the filter housing and the second filter defines an outermost surface of the filter housing.
 11. An air control valve comprising:a valve plate for controlling airflow through a main passage; a controlpassage for supplying control air to the control valve, the controlpassage including an inlet and an outlet transverse to the inlet; anouter housing supported at least partially within the control passage;an inlet tube extending from the inlet into the outer housing; a filterhousing supported within the outer housing and sealed against an outersurface of the inlet tube, the filter housing including a filter mediumfor trapping contaminants within the filter housing; and an outletpassage defined between the filter housing and the outer housing and theinlet tube and the control passage with the outlet passage being incommunication with the outlet within the control passage.
 12. The aircontrol valve as recited in claim 11, wherein the inlet tube is disposedalong an axis common with the inlet of the control passage and includesa seal for preventing contaminants from entering the inlet.
 13. The aircontrol valve as recited in claim 12, including a cap attached to an endof the outer housing that engages the filter housing to maintain adesired relative position of the filter housing within the outerhousing.
 14. The air control valve as recited in claim 13, wherein theinlet tube includes a shoulder for holding the filter housing spacedapart from the outer housing.
 15. The air control valve as recited inclaim 14, wherein the filter housing is disposed about the inlet tubeand spaced apart from an inner surface of the outer housing to define anannular passage in communication with the outlet.
 16. The air controlvalve as recited in claim 12, wherein the inlet tube includes openingsdisposed within the filter housing and defines an inlet passage from theinlet into the filter medium.
 17. The air control valve as recited inclaim 15, wherein a portion of an outlet passage is defined about theinlet tube disposed within the control passage.
 18. The air controlvalve as recited in claim 12, wherein the filter element comprises afirst filter having a first porosity and a second filter having a secondporosity different than the first porosity.
 19. A method of installing afilter comprising: installing an inlet air tube into an inlet, the airinlet tube including openings for directing airflow from the inlet;installing a filter housing onto the inlet air tube; and defining an airpassage between the inlet and an outlet about the filter housing and theair inlet tube.
 20. The method as recited in claim 19, wherein the inletis disposed within a port including the inlet and the outlet andincluding the step of installing an outer housing within the port anddefining at least a portion of the air passage about the filter housingbetween the filter housing and an inner surface of the outer housing.21. The method as recited in claim 19, wherein the inlet tube includesopenings that communicate air into a cavity defined by the filterhousing.
 22. The method as recited in claim 21, wherein the inlet tubedefines an inlet passage between the inlet and the cavity defined by thefilter housing.
 23. The method as recited in claim 20, includingmounting a cap to an open end of the outer housing that seals againstthe filter housing and the outer housing.
 24. The method as recited inclaim 19, wherein the filter housing includes at least one filter mediumdefining an outer wall of the filter housing.
 25. The method as recitedin claim 24, wherein the at least one filter medium includes a firstfilter medium having a first porosity and a second filter medium havinga second porosity different than the first porosity.